Pbodttction of hydraulic cement



is to say, to form Patented Mar. 8, 1932 In a:

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PIATE GERALD OTLEY OF SEVENOAKS, ENGLAND rnonnqnon or mnaumc'cnunn'rramming. Application flled December}, 1930,. serial no. 501,161, and inGreat B's t m, September This invention relates to the production ofhydraulic cement.

. It has heretofore been proposed to manufacture 21. Portland cement intwo stages, that a nucleus by the combination under a white heat ofMedway blue clay or equivalent aluminous compound with chalk orlimestone in'or about the proportions of one part of clay to five partsof chalk or limestone and to complete the manufacture by mixing thenucleus compound with uncalcined chalk or limestone, in or about the proportions of three parts of nucleus to one part of chalk or limestone.

The object of the present invention is to provide a further means ofmanufacturing a cheap and strong mortar or cement. i A method ofmanufacturing hydraulic cement according to the invention, consists inmixing ground 0W with a, lin derived from urnmg a mixture of ca clumcarbonate and aluminum silicate, said I clinker being ground to BritishPortland cement standard of fineness, and the added carbonate beingground to a degree of fineness not greater than that to which theclinker is ground and not suiiiciently coarse to leave any appreciableresidue on a 76 mesh per inch sieve, while the proportion of calciumcarbonate to free calcium oxide in the clinker is such as to give in themixture a ratio by weight of pure carbonate (GaCO to free calcium oxideof approximately 8: 1.

By the term free calcium oxide is meant the calcium oxide which iscontained in the tri-calcium silicate in the Portland cement clinker,and which is freed on the addition of water. Normally when water isadded to Portland cement clinker, the calcium oxide is liberated andcombines with the water to form calcium hydroxide. This reactionproduces considerable heat and causes undesir-' able cracking of thecement. Normally, in Portland cement, this free calcium oxide amounts to5-12% of the cement. If calcium carbonate is added to the cement clinkerin proportions according to the invention, the calcium oxide which isfreed on addition of water combines both with the carbonate and thewater to form calcium hydroxy carb'o-' NTI OFFICE t nate without theliberation of a detrimental amount of heat. It is intended throughoutthis specification that the term free lime or free calcium oxideshallmean calcium oxide which, on the addition of water, is liberated fromthe tri-calcium silicate present in the cement.

The clinker may be derived from calcareous material and argillaceousmaterial (e. g. clay, shale or slag) or any other silica and aluminabearing materials (e. g. blast furnace slag or the like) which have beenburned at a clinkering temperature i. e. about 1400 C. to form saidclinker.

Preferably, the proportions are so adjusted that the ratio of calciumcarbonate to aluminium silicate andfree silica used in forming theclinker is such as to give a ratio by weight of carbonate to silicateand free silica of approximately 3:1 i. e. the raw material for theclinker referably contains about 75% of calcium car onate and 25% ofaluminium silicate and free silica. i

The clinker material required for the invention differs in no way fromthe ordinary Portland cement clinker, since, to form this clinker, a 3:1mixture of carbonate to silicate and free silica may be used, and thekiln need only be at the usual temperature for forming Portland cementclinker, that is to say, about '1400 C. It is unnecessary, in formingthe clinker required for the inven tion, to use temperatures above this,pro vided the proportions 3:1 of carbonate to silicate are used. I Thecalcium carbonate and aluminium silicate are burned together atclinkering heat until a clinker is'formed and then the afore saidproportion of calcium carbonate e. g. natural limestone rock, is addedto the clinker, and a cementitious mixture formed by grinding themtogether. i

Preferably, the calcium carbonate and the clinker material are mixed bygrinding them together to a fine powder.

The amount of carbonate to be addedvaries from 20% to about 88% of thecement clinker content dependent on the purity of the lime-stone rock,the free calcium oxide content of the'clinker, and the strength andplasticity which is required in the resulting cement. The strongestresult is obtained by adding to 100 parts of cement clinker about 7parts by weight of calcium carbonate for every 1 part by weight ofcalcium oxide in the clinker. If, for example the cement clinkercontains 88 parts combined calcium oxide and aluminium silicate and freesilica and 12 parts free lime (CaO) then having added 88 parts ofcarbonate (CaGQ ;.),sthe final product is approximately 6 per cent freelime (GaO), 47 peracentcailciumrarbonate, and 47 per cent combinedcalcium oxide and aluminium silicate.

In cases, such as for plastering, where great strengthqis not required,but plasticity is important, a larger percentage 0 calcium carbonate maybe added.

A preferred form of material is that in which the ground down mixtureleaves not more than 10% residue on a 180 x180 sieve or 1% ona76x76sieve.

Although calcium carbonate and natural limestone rock are thepreferred-materials for use in the production of a hydraulic cement,according. to the invention, any natural rock containing a largepercentage of calcium carbonate may be employed.

It has been found .in practice that a ground mixture comprising theclinker and of calcium carbonate when tested according to :the Britishstandard specification for tensile strength of neat Portland cement, hasa resulting strength at seven da 5 after gauging, .of approximately .600l s. per square inch. If 85% of calcium carbonate is added totheclinker,.and the cement is subject to the test it has a resulting tensilestrength of about 250 lbs. per square inch.

.In one formofcarry'ing the invention into effect, cement clinker :(madeby'intima'tely mixing together calcareous and .argillaceous or othersilica andalumina bearing materials,.and burning them tea clinkeringtemperaturep is obtained, and, the amount of ree lime in the clinkeris-ascertained. Su' 4 posing the free lime (CaO) is found to be 12vpercent, then to the 88 parts combined calcium oxide and aluminoussilicate and-12 parts free lime, 88 parts of calcium carbonate in lumpform isadded. T'helcement clinker and added calcium; carbonate are thenground together .so that. the residue on -a 180 x 180 sieve does. notexceed 10%.

If a cement clinker is used which is .found to contain only (i per centof free lime [(0.30) then to the 94 parts combined calcium oxide andaluminium silicate and .6 parts free lime, 44 parts of calciumcarbonateis added, he. about 33% of the mixture, and the mixture groundas before.

1,;Any .knmwn aggregate, such as small stones, sand=fibre or the like,can lie-added to -the cement. Such aggregate, however, mast rbe addedafter the materials been ground, since, if the aggregate is added to thematerials before grinding, the resulting product will be useless ascement.

Where great strength is not required as in a mortar but a high degree ofplasticity, for use as a plastering material, calcium carbonate inexcess maybe added ;to ,the clinker before grinding, e. g. may beincreased to an amount equivalent to about 85% of the total .material. 3r a I If it is desired to produce a slow setting 1cement;asuitableiquantity of any well known retarder of Portland cement,such as potasl sium dichromate, boricacid,i borax sodium sulphate,potassium sulphate or calcium sulphate, or the like may be added tothemixture of cement clinker and calciinntorother carbonate,beforegrinding.

An apparatus for carrying theiinvention into effect may comprise oneconveyor system carryinglimestone rock, and another system carryingaluminiumlsilicate andfree silica to a mixer, and after-mixing, anotherconveyor system carrying the mixture to a kiln to produce the clinker,"which iscairried in turn to a grindin mill, the ground clinker assingto a mixing Ichamberwhere it is mixed with calcium carbonate which hasbeen ground in a second gzrindingnr'illi The separate grinding mills maybe em ployed in order that accurate proportions of the materials maypass to the mixing chamber, though if desired, the product of the andthe added limestone rock maybe ground in the same mill and if not thensufiiciently mixed the ground materialmay be fed to .a mixer. fMixersemployed according *to -the invention may be of the type usedfor'intimately mixing fine materials.

The manufacture of a hydraulic cement ac cording to the inventionobtains a quick setting strong cementit'ious mixture, which is cheaperto produce than they erdinarylorb land cement. f f It. is tobeunderstoodthat the success or the apgroces's according 'tothe.invention 'depen uponthe fulfillment .ofthe' conditions (a) the amountof carbonate. which is added must be. such as togiveto themixturezaratio by weight of purecanbonate to calcium oxide of approximately .8:1, otherwise ,there will either be an excess ofearbonate in the cementwhich w-ill remain uneonihincd, or same: at the tread lime will combinedirectly with the water to form calcium hydrate,- by thezce ment clinkermust be ground .tom'dinm'y British Portland cement standard fineness,that is to say, such as to leave" a residue other more than 10% uponan18Q'me-sh siev e'; and (c the ca rbona'te'nrust'notbe ground' fincrthan the cement'clinker. Unless'thesethree oonditiens are compliedwith,' 'pcor will'he ohtained andithe r'gag t wince pf What I claimis 1. A method of manufacturing hydraulic cement consisting in mixingground calcium carbonate with a clinker derived from burning a mixtureof calcium carbonate and aluminum silicate, said clinker being ground toBritish Portland cement standard of fineness, and the added carbonatebeing ground to a degree of fineness not greater than that to which theclinker is ground and not sufliciently coarse to leave any appreciableresidue on a 76 mesh per inch sieve, while the proportion of calciumcarbonate to the amount of calcium oxide which, on the addition ofwater, is liberated from the tri-calcium silicate in the clinker, issuch as to give in the mixture a ratio by weight of pure calciumcarbonate (CaCO to such liberated calcium oxide of approximately 8:1.

2. A method of manufacturing hydraulic cement according to claim 1,wherein the proportions of calcareous and argillaceous materials used informing the clinker are so adjusted that the proportion of calciumcarbonate to aluminum silicate and free silica is such as to give aratio by weight of carbonate to silicate and free silica ofapproximately 3: 1 in the clinker.

3. A method of manufacturing hydraulic cement consisting in mixing bygrinding together to British Portland cement standard of fineness,calcium carbonate and a clinker material derived from burning a mixtureof calcium carbonate and aluminum silicate the proportion of calciumcarbonate in the mixture to the amount of calcium oxide, which, on theaddition of water, is liberated from the tri-calcium silicate in theclinker, being such as to give to the mixture 2. ratio b weight of purecalcium carbonate (CaCO to such liberated oxide of approximately 8: 1.

4. A method of manufacturing hydraulic cement consisting in mixing bygrinding together to British Portland cement standard of finenesslimestone with a clinker derived from burning a 3: 1 mixture of calciumcarbonate and aluminum silicate, the proportion of limestone to theamount of calcium oxide which, on the addition of water, is liberatedfrom the tri-calcium silicate in the clinker, being such as to give tothe mixture a ratio by weight of pure calcium carbonate (CaCo to suchliberated oxide of approximately 8:1.

5. A method of manufacturing hydraulic cement consisting in mixing, bygrinding together to British Portland cement standard of fineness,calcium carbonate and a clinker material derived from burning a mixtureof calcium carbonate and aluminium silicate, the proportion of addedcalcium carbonate being 20-88% of the clinker content.

6. A method of manufacturing hydraulic cement consisting in mixin bygrinding together to British Portlan cement standard of fineness,limestone with a clinker derived from burning a 3:1 mixture of calciumcarbonate and aluminium silicate, the proportion of added calciumcarbonate being 20-88% of the clinker content.

7. Hydraulic cement formed of finely powdered mixture of calciumcarbonate and Portland cement clinker in the proportion of 8 parts ofcalcium carbonate to 1 of calcium oxide which, on the addition of water,is liberated from the tri-calcium silicate in the clinker, said clinkerhaving a British Portland cement standard of fineness and the calciumcarbonate having a fineness not greater than that of the clinker.

8. Hydraulic cement according to claim 7 comprising a powdered clinkerincluding about 12% calcium oxide which, on the addition of water, isliberated from the tricalcium silicate in the clinker, and powderedcalcium carbonate in the proportion of about 47% of the mixed material,said clinker having a British Portland cement standard of fineness andthe calcium carbonate having a fineness not greater than that of theclinker.

9. Hydraulic cement formed of finely powdered mixture of calciumcarbonate and Portland cement clinker in the proportion of about 6%calcium oxide which, on the addition of water, is liberated from thetri-calcium silicate in the clinker, and 33% finely powdered calciumcarbonate in the mixture, said clinker having a British Portland cementstandard of fineness and the calcium carbonate having a fineness notgreater than that of the clinker.

10. Hydraulic cement formed of a finely powdered mixture of limestoneand Portland cement clinker in the proportion by weight of 8 oflimestone to 1 of calcium oxide which, on the addition of water, isliberated from the tri-calcium silicate in the clinker, said clinkerhaving a British Portland cement standard of fineness and the calciumcarbonate having a fineness not greater than that of the clinker.

In testimony whereof I aifix my si ature.

GERALD OTLEY CASE.

